Porcine Mx1 as indicator of viral infection
Interferons are signaling proteins that are part of natural defenses. They alert the immune system to viral infection and induce a variety of changes in target cells. These changes are mediated by cytoplasmic proteins synthesized by the interferons themselves. Interferon-induced GTP-binding protein Mx1, also known as Myxovirus resistance protein 1, is one such protein. It is a GTPase that belongs to the antiviral response induced by type I and III interferons in the infected host. Mx proteins inhibit viruses through a GTP-dependent mechanism, therefore GTPase activity is necessary for the antiviral activity of Mx proteins.
More than 30 different proteins are induced by interferons. The monoclonal antibody AM39 recognizes the porcine Mx1 protein. Measurement of interferon-induced proteins can be used to quantify the presence of biologically active interferons (Figure 1). Mx1 is particularly attractive in this regard because it can rapidly increase to high expression levels that can reach 1% of total cytosolic protein (Horisberger 1992), and it is stable.
In the late 1980s, Mx proteins have drawn attention in host defense against influenza viruses. This was made possible by the first genetic evidence showing that Mx proteins possess intrinsic antiviral activities with specificity for certain negative-strand RNA viruses. These proteins were discovered in studies using influenza-resistant or susceptible mouse strains and isolated by subtractive methods of cDNA, which was used as a hybridization probe to isolate human homologs (MxA and MxB, respectively). Subsequently, a full-length cDNA clone encoding porcine Mx1, with an open reading frame of 663 amino acids very similar to human MxA, was isolated, sequenced, and mapped on chromosome 13.
A determination of porcine Mx1 is helpful in screening the pig population for swine influenza, which is an important disease in pig production. In general, pigs are hosts of the influenza virus as they are an intermediate host between birds and humans, which can give rise to new variants of the virus. Therefore, a rapid determination of porcine Mx1 can be used diagnostically as well as prophylactically for the treatment and management of at-risk populations.
The figure shows immunohistochemical analysis of frozen swine spleen tissue using mouse anti porcine Mx1 (product # T-3501, 1:200 dilution, Hematoxylin counterstaining) yielding strong cytoplasmic staining. Cells are stained in defined areas located in the red and white pulp in swine spleen. Copyright BMA Biomedicals / D. Eichelberger.
Available from BMA Biomedicals:
- S-1016: ELISA, for the determination of porcine Mx1 in blood and other biological fluids
- T-3501: Mouse anti porcine, clone AM39, purified antiserum
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Author: Dr. Sonia Accossato
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